Surgical stapling devices have been in existence for many years. They are routinely used in surgical procedures mainly for the purposes of effecting a wound closure. Some of the most popular applications include closing a skin incision and end-to-end or end-to-side anastomosis of internal (generally tubular) vessels such as the large bowel, etc. Current staplers are designed to deliver one or more staples in a serial fashion or a number of staples in one shot. Skin staplers, for example, deliver 30 or more staples in a serial fashion. The staples are stacked within the device and during the firing operation one staple is advanced from the stack and delivered through the head of the device. During the following cycle another staple is advanced from the top of the stack and again delivered through the head of the device and so on. In one shot devices such as a bowel anastomosis stapler the staples are prearranged in a linear or circular fashion and upon activation of the device all the staples are delivered through the head. Examples of existing prior art as described above include U.S. Pat. Nos. 4,592,498, 5,289,963, 5,433,721 and 5,470,010.
The mechanism involved in forming a staple and releasing it from its forming mechanism is common to the majority of surgical stapler devices. Generally the components include an anvil, a staple closing actuator, and a staple release mechanism. The anvil is normally positioned in front of the staple and the actuator directly behind the staple. As the actuator advances the staple against the anvil the back section of the staple deforms around both ends of the anvil thereby transforming the staple from a generally U-shape to a generally rectangular shape. At this point the actuator generally retracts and the staple is released from the anvil either as a result of the anvil moving out of position and allowing the staple to move forward, or alternatively ejecting the staple over the anvil thereby releasing it from the device.
A mechanism such as that described above, used in conjunction with a blood location tube, is described in Irish Patent Application S2000/0722. This describes a stapling device which has a generally oval cross-section blood locator tube that protrudes ahead of the device. The function of the blood locator tube is to track down over a guidewire through the tissue and into the opening in the artery. Once in the artery, blood flows back up one side of the locator tube and exits the device outside the body where the operator can see it. This indicates to the operator that the device is in place and it is safe to operate. This patent application also describes a specially designed staple (humpback staple) which wraps around the locator tube so that it can be deployed centrally across the radial opening in the artery. The benefits of using an oval locator tube and a humpback staple are that the staple is located centrally in the artery and hence the staple used need not be so large, and in turn, the dimensions of the shaft, which must accommodate the staple when in its unformed state, can be reduced, leading to less trauma to the tissue into which the shaft is introduced. A further consequence of having a generally oval or elongated cross section for the locator tube is that the tube will be more disposed to the center of the puncture than with a rounded tube. The device has a staple that straddles the locator tube, thereby increasing the likelihood of the staple closing the elongated wound at its center rather than towards one or other of the extremities of the wound.
The above device using a humpback staple has a number of disadvantages. When compared to conventional straight backed staples it can be appreciated that as the staple is formed around the anvil, the back is placed under tension, tending to cause the hump to collapse. In addition, because of the presence of the blood locator tube the anvil is reduced to individual fingers which tend to collapse inward due to lack of central support.
Furthermore, because of the position of the locator tube the staple former must be generally U-shaped in section so as to straddle it. Because of this the working fingers have a tendency to spread outward during the forming process.
It is an object of the invention to provide an improved surgical stapling device in which these disadvantages are avoided or mitigated, while retaining the benefits of centrally positioning the staple across the radial tear.